Planographic printing platess



United States Patent O PLAN OGRAPHIC PRINTING PLATES Douglas A. Newman,Glen Cove, and Allan T. Schlotzhauer, Locust Valley, N.Y., assignors toColumbia Ribbon & Carbon Manufacturing Company, Iuc., Glen Cove, N.Y., acorporation of New York No Drawing. Filed Aug. 24, 1956, Ser. N0.605,963

3 Claims. c1.101-149.z)

This invention relates to planographic printing and especially toplanographic printing plates formed by a coating on a flexible fibrousfoundation such as paper. in the preparation of plates of this characterit has been found that coating compositions including as a film-formingingredient a hydrophilic binder of the class of carboxymethyl cellulosecompounds or compounds of other polysaccharide carboxy ethers, have thehydroph-ilicoleophilic balance to give particularly good printingresults. Such coatings are rendered effective as printing surfaces whenthe film former is insolubilized, either by a reagent included in thecoating mixture, or after-applied to the dried coating. The use ofcertain appropriate reagents for insolubilization, particularly copper,iron, aluminum and chromium compounds, and especially chromiumcompounds, result in production of outstandingly good printing surfaceswhen reacted with the film former and aged for short periods, givingunder such conditions exceptionally large numbers of good quality copiesfrom the plate. Plates thus prepared and constituted, however, haveafter prolonged storage sometimes demonstrated a tendency to becomeoverly sensitive so that they pick up ink in the background areas duringprinting. Apparently this is especially the case when the plates havebeen stored under conditions of heat together with humidity. As a resultthe printing quality of plates of the type in question, while uniformlyhigh at the time of manufacture, is not predictable at a later date.

It is an object of the present invention, therefore, to provide coatedflexible planographic printing plates of the type heretofore described,but improved in such a way that the tendency to become sensitive to theink under certain storage conditions is markedly reduced or altogethereliminated.

According to commercial practice, the coatings employed on coated paperplanographic printing plates usually include one or more of variousfillers to improve their printing and especially their image-retentiveproperties. The fillers sometimes used for this purpose are china clay,barium sulphate, hydrated alumina, calcium carbonate, zinc oxide,titanium dioxide, fiuorspar, fullers earth and other similar materials.

According to the present invention, it has been discovered that, incoatings of polysaccharide carboxy ether compounds insolubilized withthe salts and compounds heretofore mentioned, the presence in particularof an oxide of zinc, titanium, magnesium or calcium, or mixtures ofthese particular oxides, in the composition in contrast to the othermaterials currently used as fillers, in some manner not altogetherunderstood at present, has a pronounced inhibiting effect on thetendency of the coatings to become sensitive with age. It is found that,regardless of storage conditions of heat and humidity, the plates whichinclude, as a significant portion of the filler, one or more of theoxides named will be uniformly usable and capable of producing copies ofacceptable grade after a period of aging.

The present invention, therefore, is characterized by the presence of anaging sensitization inhibitor in the form 2,4i',466 Patented June 21,196Q of material selected from the group consisting of the oxides ofzinc, titanium, magnesium and calcium and mixtures thereof, as asignificant portion of the filler in coat ings of the polysaccharidecarboxy ether type, insolubilized by salts or compounds of copper,aluminum, iron and chromium, and especially compounds of chromium.

Other features and advantages will hereinafter appear.

'In practicing the present invention, a flexible paper foundation sheetis preferably treated in a known manner with wet strength-impartingingredients such as melamine formaldehyde, although this may bedispensed with in the preparation of plates for certain short-runpurposes. Likewise, known surface sizings or water-barrier coat-ings maybe applied which provide for improved operation under long-runconditions. When such preliminary preparations, if any, are completed,the paper is coated on at least one surface with one or more coats of aplanographic surfacing composition.

For this purpose an aqueous suspension or slurry is prepared containingbetween one and five percent of a film-forming constituent such ascarboxymethyl cellulose,

' or other polysaccharide carboxy ether, such as the carboxy ethers ofstarch, or carboxy ethers of the watersoluble gums containing saccharidunits, such as gum arabic, gum tragacanth, mesquite gum, larch gum, etc.In addition, the suspension includes a filler which may be about twotofour times the weight of the binder present. Heretofore this fillerhas often consisted entirely of china clay or the like, but according tothe present invention, at least a certain percent of the filler iscomposed of an aging sensitization inhibitor in the form of an oxide ofzinc, titanium, magnesium or calcium, or a mixture of two or more ofthese materials. Other ingredients may be included to aid, for example,in the coating operation, or for other special purposes, but theingredients enumerated are the essentials. The slurry is applied to thepaper, for example by a brush coating operation, and allowed to dry.

One example of a coating suspension for this purpose is:

Formula I Ingredients: 7 Parts by weight 5% aqueous dispersion of sodiumcarboxymethyl cellulose China clay 15 Zinc oxide 5 Glycerine- -n 3 Whenthe coating is substantially dry, the coated surface of the sheet istreated, as by tub sizing, with an aqueous solution of one or more ofthe metal salts or com pounds heretofore mentioned. For best results amixture of chlorides or sulfates of aluminum, ferric iron and copper,together with chromium trioxide, are employed as disclosed in the patentto Douglas A. Newman, No. 2,655,864. The preferred formula as shown insaid patent is as follows:

Formula II Percent Copper sulphate 3 Aluminum sulphate 1 Ferric chlorideChromium trioxide This treament renders the coating insoluble in water,and the dried coating will then accept and retain imaging material andprint copies of high quality when used the plate or master in aplanographic printing process.

While the two step treatment of the printing surface is very effective,there has also been discovered a means whereby substantially equivalentprinting quality can be achieved using a single coating formula whichautomatically becomes insoluble on drying, and the present inaga nst:

of the invention is as follows:

.SQ nm a b m h s u ase -5 Water' cc .78 Methanol cc .12 C a :a p .7-Zinc oxide d o 2.5 Glycerine do 1.0 5% ammoniacal coppersnlphate cc 40Ammonium" dichron a g, Cl. "gra ns-.. 1.0 Ferric ammonium citrate, U.S.P. ;.do 1.5

The slurry of Formula'IIIis applied tothe paper web, as by brushcoating, and allowedto a pma asl the application of'heat, to give acoating is water insoluble and provides a planographic printingsurfaceofgood quality. j

It can be seen that both the form of the invention exemplified byFormulas I and Hand that exempiified by"Formula HI relate topolysaccharide carboxy ether coatings which are rendered insolublc by aparticular group of metal salts or compounds, and including 'especially,although not necessarily,'a compound of chromium. The plates thusconstituted may be aged for extended periods, even under adverseconditions ofrhigh temperature and humidity, and may then hesuccessfully imaged and used to print copies of goodquality Q'Ifhetendency heretofore experienced for the reaction product ofinsolubilization treating materials such as copper, aluminum or ironsalts or chromium compoundsjwith film formers of the polysaccharidecarboxy'ether type to become increasingly ink sensitive with prolongedaging, presumably due to sustained subjection to heat and humidity, isfound to be effectively inhibitedby the prescnce of the special oxidefiller which acts to maintain the originally manufactured vand normallyaged condition of the plate surface, free from. unusual ink sensitivity,regardless of the duration and temperature-humidity conditions ofstorage which the plate may encounter.

' Formula I and Formula III have been presented showing thedesensitization inhibitor as zinc oxide and represent the form of theinvention at present preferred from the standpoint of cost andavailability. Itwill be understood, however, that formulas which differfrom these essentially by a substitution of a substantially equal amountof titanium dioxide, magnesium oxide or calcium oxide, or of such of themore complex oxide compounds of these metals, e.g. peroxides orsesquioxides, as are commercially available, or any mixture thereof, areequally good examples of the invention and will provide compositionsdemonstrating in full the stated advantages.

The proportion of the special oxidefiller which should be included mayvary, but it has been found that the use of amounts equivalent to aboutthirty percent of the weight of the film former present will produceclearly noticeable etfects for the purpose. In most cases it appearsthat no particular advantage accrues from including amounts in excess ofthe weight of film forming material although more maybe used if desiredwithout substantial detriment.

-W h ile the invention herein has been described with particularreference to incorporation 0f the special oxide filler directly in thepolysaccharide carboxy ether coating mix, it has also been foundthat i-fthe' same is included instead in a coating which directly underlies thepolysaccharide carboxy ether coating, thelsensitization inhibitingadvantagesheretoiore set out will beattained to a substantially equalextent. when the ial oxide filler is thus incorporated, it appearsithats' ewhat'less than all of the special oxide materialused; is effective.Accordingly the amountto be employed maybe calculatedon the basis ofwhatamount would give the desired results if placed directly in thesurface coating planned, and then preferably using a somewhat increasedamount in the undercoating. For this purpose, an increase of betweenfi-fty percent and one hundred percent above the amount of special oxidefiller which would have been used in the surface coating is at presentrecommended. It .wnrbe' appreciated also thatalportion of thespecialoxide filler may be includedin both coatings if desired withequivalent'beneficial effect. In Iact the m n o th ee px'u file in an faa nf a printing surface layerc'onsisting of the printing surfacecoating and the coating, if any, directly underlying it will give aresult demonstrating the beneficial'efiect heretofore noted.

Variations and modifications: may be made within the scope of the claimsand portions of the improvementsmay be'used without others. l i 7 Weclaim:

1. A planographic printing plate comprising a fibrous flexiblefoundation web; a'p'rinting surface 'coating 'on said'webconsistingessentially of an insoluble {hydrophilic polysaccharide carboxy ether'film- Iorriiing niaterial insolubilized by reaction with a metalcompound selectedfrom the group consisting of coppensaltgiron salts,aluminum salts and chromium compounds which thus reacted has ahydrophilic-oleophilic balance suitable for direct -irnaging use, andwhich is subje :to becoming excessively ink-sensitive upon subsequentexposure to protracted conditions of abnormal heat and humidity, saidcoating including an amount of zinc oxide 'suflicient to act as an agingsensitization inhibitor for said insolubilized film former, said amountbeing equivalent to at least about thirty percent of the weight of'saidforming material.

2. A planographic printing plate comprising a fibrous flexiblefoundation web; a printing surface coatin gon said Web consistingessentially of an insoluble'hydro philic polysaccharide carboxy etherfilm formin'g material insolubilized by reaction with metal'conipoundsconsisting of copper, iron and aluminum saltsfand 'a chromium compoundand which thus reactedjha sl a hydrophilic-oleophilic balance suitablefor direct-imaging use, and which is subject to becoming excessivelyink-sensitive upon subsequent exposure to protracted conditions fabnormal heat and humidity, said coating including a quantity of inertfiller and a sufiicient amount ofjzinc oxideto act as an agingsensitization inhibitor for said insolubili z ed film former, saidamount being equivalenbto at least about thirty percent of the weight ofsaid film forming material.

3. A planographic printing plate comprising a fibrous flexiblefoundation web; a printing surface coating on said web vconsistingessentially of an insoluble hydrophilictpolysaccharide carboxy etherfilm torming materi al insolubilized by reaction with m etal compoundsconsisting of copper, iron and aluminum'salts; and ;a chromium oxidecompound and which when-thus reacted has a hydrophilic-oleophilicbalance suitable for direct-imaging use, and which is subject tobecoming. .excessively ink-sensitive upon subsequent exposuretoprotracted conditions of abnormal heat and;hum idity, said coatingincluding a filler which is an aging s'ensitization inhibitor, saidinhibitor being zinc oxide present in ,an amount equal to at least aboutthirty percent -oflthe weight-of said'film forming material.

References Cited in the fileof this patent UNITED STA'IES PATENTS2,542,784 Van Dusen Feb. 20, l 91 2,598,189 Q425 2,635,537 Apr.'2 7,1953 2,655,864 r 1 r1 2,693,145 Mullen f Nov. 2, 19 5 1 2,778,301Brinnick et al. Ian. 22, 1957

1. A PLANOGRAPHIC PRINTING PLATE COMPRISING A FIBROUS FLEXIBLEFOUNDATION WEB, A PRINTING SURFACE COATING ON SAID WEB CONSISTINGESSENTIALLY OF AN INSOLUBLE HYDROPHILIC POLYSACCHARIDE CARBOXY ETHERFILM FORMING MATERIAL INSOLUBILIZED BY REACTION WITH A METAL COMPOUNDSELECTED FROM THE GROUP CONSISTING OF COPPER SALTS, IRON SALTS, ALUMINUMSALTS AND CHROMIUM COMPOUNDS AND WHICH THUS REACTED HAS AHYDROPHILIC-OLEOPHILIC BALANCE SUITABLE FOR DIRECT-IMAGING USE, ANDWHICH IS SUBJECT TO BECOMING EXCESSIVELY INK-SENSITIVE UPON SUBSEQUENTEXPOSURE TO PROTRACTED CONDITIONS OF ABNORMAL HEAT AND HUMIDITY, SAIDCOATING INCLUDING AN AMOUNT OF ZINC OXIDE SUFFICIENT TO ACT AS AN AGINGSENSITIZATION INHIBITOR FOR SAID INSOLUBILIZED FILM FORMER, SAID AMOUNTBEING EQUIVALENT TO AT LEAST ABOUT THIRTY PERCENT OF WEIGHT OF SAID FILMFORMING MATERIAL.